The ultrasonic diagnostic apparatus transmits an ultrasonic wave into the inside of the object by an ultrasonic probe including plural ultrasonic transducers, receives a reflected echo signal of the ultrasonic wave corresponding to the structure of body tissue from the inside of the object, generates a tomographic image, for example, a B-mode image on the basis of the reflected echo signal, and displays the B-mode image for diagnosis.
In such an ultrasonic diagnostic apparatus, generating three-dimensional tomographic image volume data from reflected echo signals of plural tomographic planes of the object measured by ultrasonic scanning in a short-axis direction of the ultrasonic probe and generating an image (three-dimensional tomographic image) by projecting the three-dimensional tomographic image volume data onto the two-dimensional projection plane using a volume rendering technique are known.
The volume rendering technique is to generate a three-dimensional tomographic image by performing cumulative addition of the brightness values of plural voxels, which are arrayed in the line-of-sight direction when the three-dimensional tomographic image volume data is viewed from a point on the two-dimensional projection plane, along the line-of-sight direction and setting the result as a pixel value (brightness) of the two-dimensional projection plane while correcting the brightness values by transparency/opacity of each voxel, for example.
On the other hand, the brightness of each voxel obtained by ultrasonic scanning is determined according to the acoustic impedance of tissue in the object, ultrasonic attenuation due to propagation in the object, and the like. For this reason, it is difficult to generate a three-dimensional tomographic image which characterizes only specific tissues to be diagnosed (for example, with enhanced brightness).
In order to cope with such a problem, for example, a maximum value projection method of displaying only high-brightness tissue of the three-dimensional tomographic image volume data or a minimum value projection method of displaying only low-brightness tissue is generally used. In addition, as disclosed in PTL 1, reversing the brightness level of a B-mode image so that the three-dimensional structure of a low echo region can be easily viewed is known.